The theory of operation of a magnetic flow meter (‘magflow meter’) is based on Faraday's law of induced voltage, wherein an electromotive force (EMF) is produced that is proportional to the velocity of a conducting medium that flows through a magnetic field. Typically, in the case of a magflow meter, the flowing medium is a conductive medium passed through a section of conduit that is subjected to a transverse magnetic flux. As the conductive fluid passes through the conduit, the resulting EMF is detected by electrodes that are mounted to the conduit walls and in physical contact with the medium. To prevent shorting of the EMF, the conduit walls are constructed of a non-conductive material.
Magflow meters have found application in the process control industries (chemical, food-and-beverage, pulp and paper, water treatment) because they have low measurement error (0.2% of reading attainable) over a broad range (typically 30:1) and they require no moving parts (unlike turbine meters or paddlewheel technology) or flow restriction (unlike differential pressure meters) to operate. Magflow meters can also be configured to resist the deleterious effects of the harsh chemicals of the flow stream medium through proper selection of the materials for the electrodes and conduit walls.
Previous designs have utilized a conduit fabricated from a non-conducting material to provide the desired electrical isolation. The electrodes are mounted so that the tips are flush with the interior wall. Other designs have implemented a conduit constructed of a non-conducting liner within a metallic outer housing, with the tips of the electrodes protruding into the flow stream.
Various prior art designs possess certain disadvantages that prevent the realization of the full benefits of the magflow meter. Most magflow meters utilize a dielectric sleeve within a metal housing. Outfitting a metal housing with a dielectric liner is a costly process. Current magflow meters are complicated assemblies requiring hardware to be welded or otherwise attached to the metal housing for the mounting of the electrode and electromagnetic assemblies. Furthermore, these approaches typically teach the use of metallic electrodes, which are incompatible with applications and processes in other industries.